A Periodic Table Group 13 metal nitride semiconductor represented by gallium nitride has large band gap, and interband transition is a direct transition. Therefore, the Periodic Table Group 13 metal nitride semiconductor has been put into practical use as light emitting elements at relatively short wavelength side such as ultraviolet or blue light emitting diodes and semiconductor lasers. In addition, the production of the gallium nitride substrates used in these devices has also been realized as a consequence of developments in crystal growth technology in recent years.
Silicon and oxygen are known as dopants that make Periodic Table Group 13 metal nitride semiconductor crystals into the n-type, and it is known that doping can be carried out when a Periodic Table Group 13 metal nitride semiconductor crystal is produced by a vapor-phase growth method by feeding, e.g., silane gas (SiH4), into the growth atmosphere as a silicon source and by feeding, e.g., water or oxygen, into the growth atmosphere as an oxygen source. However, facial selectivity has been reported to occur in the doping of oxygen into gallium nitride, and it is known that the incorporation of oxygen is impaired in epitaxial growth for which the growth plane is the C-plane and a satisfactory oxygen doping cannot then be achieved (refer to Patent Document 1). As a consequence, results have been reported of a large amount of silicon doping for gallium nitride crystals obtained by C-plane growth and a large amount of oxygen doping for gallium nitride crystals for which the growth plane is a crystal plane other than the C-plane (refer to Patent Documents 1 and 2).
In addition, for gallium nitride crystals obtained by facet growth on a base substrate for which the C-plane is the main surface, the results have been reported of a large amount of oxygen doping at the facet growth region and a large amount of silicon doping at the C-plane growth region (refer to Patent Document 3).
When, on the other hand, a Periodic Table Group 13 metal nitride crystal is used for a light-emitting device, it must be capable of efficiently emitting light when used in the device, and the production of a crystal in which there are few crystal defects is required in order to improve the efficiency of light emission. Problems with Periodic Table Group 13 metal nitride semiconductor crystals include the problem of spontaneous polarization and the problem of a reduction in the internal quantum efficiency due to the occurrence of piezoelectric polarization. The problem, inter alia, of the reduction in the internal quantum efficiency could be solved if a crystal could be formed on a nonpolar plane of a Periodic Table Group 13 metal nitride semiconductor crystal, but the current situation is that it is very difficult to bring about the epitaxial growth of a Periodic Table Group 13 metal nitride semiconductor crystal having a low stacking fault density on a nonpolar plane or a semipolar plane.
To respond to this problem, the formation on the substrate of an intermediate layer containing, for example, carbon and aluminum, has been proposed (refer to Patent Document 4).
In addition, a method has been proposed in which a Periodic Table Group 13 metal nitride semiconductor crystal having little surface unevenness is produced by growing the Periodic Table Group 13 metal nitride semiconductor crystal on a seed in a solution containing the element nitrogen and a Periodic Table Group 13 metal in a molten salt wherein a semipolar plane is the main surface of the seed (refer to Patent Document 5).
[Patent Document 1] Japanese Patent Application Laid-open No. 2000-044400
[Patent Document 2] Japanese Patent Application Laid-open No. 2006-240988
[Patent Document 3] Japanese Patent Application Laid-open No. 2010-070430
[Patent Document 4] Japanese Patent Application Laid-open No. 2010-030877
[Patent Document 5] Japanese Patent Application Laid-open No. 2011-178594